A. Field of Invention
This invention pertains to the art of methods and apparatuses regarding crossbow drawing mechanisms and more specifically to methods and apparatuses regarding crossbow drawing mechanisms which utilize a clutch device for preventing damage to the crossbow drawing mechanism that may occur from attempts to overdraw the crossbow.
B. Description of the Related Art
It is known in the art for archery devices to include a bow having two outwardly extending arms and a bowstring strung between the ends of the outwardly extending arms. Conventionally, in order to propel or “fire” a projectile, such as an arrow, from the crossbow, the user grasps the bow in approximately the center between the two outwardly extending arms and pulls back or “draws” the bowstring with one hand while at the same time pushing the bow away with the other hand Drawing the bowstring requires a certain amount of strength and can, over time, take a physical toll on the user's arms. The amount of force needed to draw a given bow is normally measured in pounds and is known as the “draw weight” of a bow. Upon release of the bowstring from this “drawn” position, potential energy in the bowstring is imparted upon the projectile and the projectile is propelled or fired.
It is known to increase the speed and accuracy at which a projectile is propelled or fired from the crossbow by increasing the draw weight or the stiffness of the outwardly extending bow arms. However, an increase in the draw weight directly results in an increase in the amount of effort a user must exert to pull or draw the bowstring into position for firing. Modern crossbows can have bowstring pull weights of 150 pounds or more. It is readily apparent that with high pull weights, even operating a crossbow could be difficult, if not impossible, for many users having limited physical strength. This is particularly true for target practice or other situations where the crossbow may be drawn numerous times.
Recently, crossbows include devices for assisting the user in drawing the crossbow. For example, some crossbows include a stirrup bracket mounted on one end of the crossbow. In such crossbows, the user places the stirrup bracket onto the ground and places a foot in the stirrup bracket. By applying the user's body weight to the grounded stirrup bracket, the user can pull up or draw the crossbow bowstring into the “cocked” position. Although helpful, this provides only limited advantage. It is known to provide a leverage type cocking device to a crossbow. These crossbows typically comprise an arm which is pivoted to pull or push the crossbow bowstring into the cocked position. Additionally, it is known to utilize pneumatic or fluid actuated pistons to cock the crossbow bowstring into position for firing. Still other crossbows utilize ratchet or pulley arrangements mounted to the frame of the crossbow.
Although these methods work well for their intended purpose, several disadvantages exist. A significant problem relating to the cocking of a crossbow bowstring, whether performed manually or by means of a bowstring drawing mechanism, is found in properly withdrawing the bowstring relative to the outwardly extending limbs of the crossbow. A properly drawn bowstring should impart an equalized force to the projectile or arrow positioned therein when the bowstring is release from the crossbow trigger mechanism. This balancing of forces imparted on the bowstring by means of the crossbow limbs is particularly important for shooting accuracy in using the crossbow as well as for safety of use. Additionally, although these known systems attempt to simplify the bowstring cocking procedure, typically, they add complexity or cost, or are cumbersome to handle and use effectively.
To address the disadvantages listed above, crossbow bowstring drawing mechanisms, such as the one disclosed in U.S. Pat. No. 6,095,128 titled Crossbow Bowstring Drawing Mechanisms, which is herein incorporated by reference, have been developed. Known crossbow drawing mechanisms can be integrated into or secured in the crossbow stock member and provide a straight and balanced draw to the crossbow bowstring to cock the crossbow. The crossbow drawing mechanism can be either manually operated or motorized. The crossbow drawing mechanisms utilizes a source of rotational power such as a hand crank, power screwdriver, or an electric motor and a bowstring engaging device, commonly referred to as a claw member, to draw the bowstring.
Typically, to remove a bowstring engaging device 400 of a bowstring drawing mechanism 410 from a storage position, shown in FIG. 7, a user must disengage a safety lever 401, lift the bowstring engaging device 400 from the storage position, and then connect the bowstring engaging device 400 to the bowstring 403, as shown in FIG. 8. Commonly, the draw cord 402 of the bowstring engaging device 400 is under tension while the bowstring engaging device 400 is in the storage position. Therefore, to properly disengage the safety lever 401, the tension in the draw cord 402 must be relieved. The safety lever 401 may prevent a drive shaft 404 from rotating in a first direction while allowing the drive shaft 404 to rotate in a second direction. The tension in the draw cord 402 can be relieved by applying a slight amount of pressure to cause the drive shaft 404 to rotate in the second direction as if attempting to increase the tension applied to the draw cord 402. A hand crank 405 may be used to apply the slight amount of pressure to the drive shaft 404 necessary to allow the transfer of the retention force away from the safety lever 401 thereby allowing the safety lever 401 to be properly disengaged, as shown in FIG. 9.
Commonly, to properly draw the bowstring 403, a second safety device 406 must be disengaged or moved to the “Fire” position. With the second safety device 406 disengaged, the drive shaft 404 is then rotated thereby causing the bowstring engaging device 400 and the bowstring 403 to be retracted and drawn respectively. The user may determine that the crossbow is cocked when the second safety device 406 is caused to be engaged or moved to the “Safe” position and when the string latch of the trigger assembly 407 is heard engaging the bowstring 405. Typically, once the bowstring engaging device 400 has drawn the bowstring 403 and the crossbow is cocked, the bowstring engaging device 400 retains the bowstring 403 under tension rather than the string latch of the trigger assembly 407. To relieve the tension applied to the bowstring engaging device 400, the drive shaft 404 must be slightly rotated in the second direction, thereby allowing the safety lever 401 to be disengaged so that the bowstring engaging device 400 can be moved forward, towards the string latch, such that the tension from the bowstring 403 is now applied to the string latch. The bowstring engaging mechanism 400 may now be slid out of the trigger assembly 407 and returned to the storage position. The drive shaft 404 may then be rotated in the second direction to retract any excess draw cord 402 and to secure the bowstring engaging mechanism 400 in the storage position by applying tension to the bowstring engaging device 400.
A user may significantly damage a crossbow drawing mechanism by “over-cranking” or excessively rotating the drive shaft when attempting to disengage the safety lever. Over-cranking the crossbow drawing mechanism may damage the crossbow and/or over-stress the draw cord. The crossbow drawing mechanism typically utilizes a gear-reduction mechanism that allows the user to exert a minimal amount of force in drawing the crossbow. Therefore, over-cranking combined with the gear-reduction mechanism can result in the trigger mechanism being forcibly lifted from its mounted position in the barrel of the crossbow and/or the draw cords being broken. What is needed then is a crossbow drawing mechanism that provides a straight and balanced draw to the crossbow bowstring to cock the crossbow while preventing the over-cranking of the crossbow drawing mechanism.